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Early Resultws from a Broad Compatibility Study of Various Materials with Ionic Silver Biocide - 2020
Early Resultws from a Broad Compatibility Study of Various Materials with Ionic Silver Biocide - 2020.pdf
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Summary:

The study evaluated ionic silver biocide (AgF solution, 400 ppb) for spacecraft potable water systems, focusing on how much silver is lost to different materials over time.

Metals

  • Titanium (Grades 2 & 5), Inconel 718, 316L stainless steel, Aluminum 6061/7075: All showed >97% silver uptake within 1 week, meaning nearly all silver ions were depleted from solution.
  • Conclusion: Metals are highly incompatible with silver biocide unless special coatings or treatments are applied.

Polymers

  • Best performers (low silver loss, <10%):
    • PMMA (Acrylic): ~0% uptake.
    • Polypropylene (PP): ~3%.
    • PVDF (Kynar®): ~6%.
    • PVC: ~6%.
    • PEEK, Ultem (PEI), Ultem 9085 (3D print filament): 9–12%.
    • ETFE, FFKM, PTFE (Teflon™) also performed well.
  • Poor performers:
    • EPDM & Viton (synthetic rubbers): >97% silver loss.
  • Conclusion: Most polymeric materials are highly compatible with silver biocide, making them strong candidates for spacecraft water systems.

Ceramics

  • 99.8% Alumina & Synthetic Sapphire: Minimal uptake (~0.3–1%).
  • Magnesia Partially Stabilized Zirconia (MSZ): ~74.5% uptake, poor performance.
  • Conclusion: Certain ceramics are excellent choices for long-term silver compatibility.

Tubing

  • Tygon Chemical® tubing: Only 2% silver loss, best performer.
  • PharmaPure® tubing: Also advanced to longer-term testing due to low silver uptake and low organic leaching.
  • Conclusion: These tubing materials are ideal for ground testing and simulation systems.

Best Usages with Other Materials

  • Metals need coatings (e.g., passivation, electropolishing, polymer coatings) to reduce silver loss.
  • Polymers and select ceramics are the best base materials, with Ultem, PEEK, PMMA, polypropylene, and sapphire being prime candidates.
  • Tygon Chemical® tubing is highly compatible for circulation systems, minimizing silver depletion and contamination.
  • Overall, spacecraft systems should rely more on engineered polymeric wetted materials rather than metals for preserving silver biocide effectiveness.